A Streatham banker named Mr Alexander Holder makes a loan of £50,000 (equivalent to approximately £5.76 million in 2019[1][2]) to a socially prominent client, who leaves a beryl coronet - one of the most valuable public possessions in existence - as collateral. Feeling his bank's personal safe is insufficient to protect such a rare and precious piece of jewellery, he takes it home and keeps it in his dressing room. However, he and his niece Mary later find his son Arthur holding the coronet, seemingly trying to bend it, and three beryls missing from it. A panicked Holder seeks out Sherlock Holmes for help.

Despite the damning evidence against Arthur, who is refusing to give a statement, Holmes is unconvinced. With the threat of Holder's reputation being besmirched and a national scandal weighing heavily on his mind, Holmes determines Arthur could not have broken the coronet on his own without making noise, notices footprints in the snow outside Holder's home, and considers Holder's servants, Mary, and Arthur's rakish friend Sir George Burnwell as potential suspects.